A polyaxial bone screw to be connected with a stiff rod, usually made of metal, is known from DE 43 07 576 C1. When using a flexible rod made of an elastic material with such a bone screw, the pressure exerted by the inner fixation screw onto the rod would cause a deformation of the elastic material which could result in loosening of the fixation.
Bone anchoring devices comprising a bone screw and a flexible rod which is made of an elastic material are known from EP 1 364 622 A2 and EP 1 527 742 A1. The rod and the receiving part of the bone screw as well as the closure element comprise geometrically corresponding ribs and grooves in the surface to achieve a form-fit connection. Before fixation, the geometrically corresponding shapes of the rod and the bone screw have to be aligned. This makes the adjustment difficult and time consuming. Furthermore, the receiving part and the shaft of the bone screw are monoaxially connected which further limits the possibility of adjustment of the position of the shaft relative to the rod.
Based on the foregoing, there is a need for a bone anchoring device which can be used with a flexible connection element made of an elastic material and which allows a polyaxial adjustment of the position of the bone anchoring element relative to the rod while simultaneously providing a safe locking.